Optical fibre material comprising silica-based glass with reduced photo darkening

48) A high power amplifier comprising:

• a) a diode bar array pump laser which operates at a wavelength λpump and with a pump power exceeding 5 W,
• b) a coupling device,
• c) a silica host glass fibre with a rare earth doped core co-doped with network modifiers aluminum and/or boron and phosphor in a concentration such that the total atomic network modifier concentration is at least 7 times the rare earth atomic concentration and
• d) a silica host glass fibre with a rare earth doped core co-doped with network modifiers aluminum and/or boron and phosphor in a concentration such that the total atomic concentration of rare earth and aluminum and/or boron is substantially equal to the atomic concentration of phosphorous
• e) an output delivery fibre
• f) wherein the wavelength λpump is resonant with said rare earth doping absorption band

57) A waveguide laser or amplifier material comprising

• a) a silica glass host material,
• b) one or more rare earth elements in total concentration cRE at. % (mol.),
• c) one or more network modifier elements selected from the group of tri- or penta-valent atoms of the periodic table of the elements in total concentration cNME at. % (mol.),
• wherein the the ratio of atomic concentrations of the modifier elements to that of the rare earth elements cNME/cRE is larger than 5, and
• wherein the total atomic concentration of rare earth and the tri-valent network modifiers is substantially equal to the atomic concentration of the penta-valent network modifier.